1. Field of the Invention
This invention presents modifications and improvements to conventional projectile launch simulation devices. These devices are used to simulate the translational and angular accelerations encountered by projectiles during launch from rifled gun barrels. The simulation process is known as the Reverse Ballistic Launch Simulation Method (RBLSM) and consists essentially of the following two events.
1) the setback event (to simulate translational accelerations by means of rapidly decelerating a backwards oriented projectile), and
2) the spin event (to simulate angular accelerations resulting from projectile engagement with the lands and grooves of a rifled barrel by applying torque to a non-spinning projectile). Assemblies designed to perform these simulations are referred to herein as xe2x80x9cspinnersxe2x80x9d.
During simulation operations, a conventional spinner is designed to expel a component referred to as a momentum exchange mass (MEM) from the spinning impact containment chamber, referred to as the catch tube. The projectile""s transferred linear momentum results in the deceleration of the projectile (to zero translational velocity in a successful operation) and the MEM being expelled from the rear opening of the catch tube (with a fraction of the projectiles impacting velocity). The modified spinner design contrasts the conventional design by introducing a translational degree of freedom for the catch tube. Modifications to the catch tube configuration results in a single entrance for the projectile, mitigator, and MEM as opposed to the open rear design of conventional catch tubes. The modification to the catch tube as well as the additional degree of freedom eliminates passage of any or all components through the catch tube as a consequence of the impact event.
2. Discussion of Related Art
A conventional spinner system is depicted in FIG. 1. Currently, spinners used to perform the RBLSM consist of, but are not limited to, the following components: catch tube 1, mitigator 2, momentum exchange mass 3, stationary catch tube support bearings 4, and drive train/brake system 5. In typical operations, the catch tube 1 is loaded with the mitigator 2 and the momentum exchange mass 3 as shown in FIG. 1. The drive train 5 is powered up resulting in the transmission of torque to the catch tube 1. The applied torque results in spinning the catch tube 1 about the bore axis 6 at a pre-selected rate of revolutions per unit time. The projectile 7 enters the forward end of the catch tube 1 and impacts the mitigator 2. The mitigator 2 begins to deform thereby decelerating the projectile 7 as well as dissipating some quantity of the projectile""s 7 translational kinetic energy. The mitigator 2, while spinning at the same rate of revolutions per unit time as the catch tube 1, begins to transfer torque to the projectile 7. This applied torque results in increasing the angular velocity of the projectile 7 up to a desired rate thereby eventually achieving a post impact equilibrium angular velocity with the catch tube 1. Both mitigator 2 deformation and torque transmission to the projectile 7 requires the support of an inertial mass as provided by the momentum exchange mass 3. Without the momentum exchange mass 3, the mitigator would be pushed through the catch tube 1 without appropriately decelerating or spinning up to the required rotation rate.
The purpose of the catch tube 1 is to remain stationary (with regards to translation along the projectile""s 7 flight path) and to act as a guide, or path constraining device for the projectile 7, mitigator 2 and MEM 3 throughout the impact and deceleration (acceleration) events. Typically, in conventional spinners, the MEM 3 exits the catch tube 1 while the mitigator and projectiles remain in the catch tube (as their translational velocities have become zero due to the momentum transfer and kinetic energy exchange occurring during impact).
To simulate the setback event, in which translational accelerations are applied to the projectile 7, the momentum exchange mass 3 functions as an inertial mass against which the mitigator 2 is supported (from rearward translational motion) by means of the MEM""s 3 inertial resistance. The inertial resistance to motion supplied by the momentum exchange mass 3 results in the deformation of the mitigator 2 and the deceleration of the projectile 7 at or near empirically determined rates. The linear momentum of the projectile 7 however, is conserved and is transferred through the mitigator 2 to the momentum exchange mass 3. As a consequence of the transferred momentum, the MEM 3 takes on a translational velocity collinear with that of the projectile 7 and exits the rear of the catch tube 1. A successful setback event for a non-spinning projectile is one in which the translational deceleration of the test projectile 7 is equal to, (in terms of magnitude and duration) but of opposite sign, as the translational acceleration(s) of an actual gun launched projectile.
To simulate the spin event, the MEM 3 provides the necessary inertial resistance to translational motion of the mitigator 2 thereby assuring axial deformation of the mitigator 2 (i.e. kinetic energy absorption and linear momentum exchange) during the impact event. The projectile 7, in contact with the mitigator 2 during the impact event, begins to rotate due to the interface friction between the mitigator 2 and projectile 7. The spin rate of the projectile is a function of the interface friction forces. The instantaneous angular velocity of the projectile 7 changes from what was initially zero revolutions per unit time (as test projectiles are generally launched from smooth bore gas-guns) to the final catch tube 1 rotation rate.
A successful application of the RBLSM involves precise control of both the transferred angular momentum and the linear deceleration rate. Ideally, the simultaneous occurrence of the setback and spin events closely simulate the effective accelerations encountered in actual gun launch. Total acceleration of the projectile is the instantaneous vectorial sum of both translational deceleration and angular acceleration. The control and adjustment of these rates are achieved by choosing the appropriate mass for the MEM 3, selecting the appropriate mitigator 2 material, and by custom profiling conical tips (impact/friction surface) on the mitigator 2.
The invention features a modified catch tube component capable of performing the function of the conventional catch tube and the conventional MEM simultaneously. The catch tube will also feature a capability to accept modular units of mass for adjusting the available angular momentum (of the spinning catch tube) as well as to incrementally adjust inertial resistance for controlling post-impact translational motion. The safety and performance enhancements of the modified spinner are achieved by the above mentioned integration of the MEM with the catch tube. This invention will eliminate MEM free flight and prevent excessively soft, or excessively hard projectile impacts. Equipment such as rails and wheel sets are used to assure that the motion of the catch tube is constrained to translation (a degree of freedom collinear with the catch tube bore axis) and to rotation (a degree of freedom about the catch tube bore axis). The invention differs from conventional spinners in that the motion of a conventional catch tube is limited to rotation only and the MEM to translation and rotation (along and about the bore axis respectively).